1. Technical Field
The present invention relates to a modulation apparatus and a test apparatus.
2. Related Art
Conventional LINC circuits that output modulated signals are known, as shown in Non-patent Documents 1 to 5. These LINC circuits add together two periodic signals having fixed amplitudes and different phases in order to output a modulated signal with the desired amplitude and phase. These LINC circuits can output modulated signals having large amplitudes and little distortion, regardless of the linearity of the amplifiers at the output stage.    Non-patent Document 1: Lars Sundström, “Spectral Sensitivity of LINC Transmitters to Quadrature Modulator Misalignments”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 49, NO. 4, JULY 2000    Non-patent Document 2: Fernando J. Casadevall and Antonio Valdovinos, “Performance Analysis of QAM Modulations Applied to the LINC Transmitter”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 42, NO. 4, NOVEMBER 1993    Non-patent Document 3: Gwenael Poitau, Ahmed Birafane and Ammar Kouki, “Experimental Characterization of LINC Outphasing Combiners'Efficiency and Linearity”, IEEE Radio and Wireless Conference, 2004    Non-patent Document 4: Young Yun Woo, Jaehyok Yi, Youngoo Yang, and Bumman Kim, “SDR Transmitter Based on LINC Amplifier with Bias Control”, Microwave Symposium Digest, 2003 IEEE MTT-S International    Non-patent Document 5: Xuejun Zhang, Lawrence E. Larson, and Peter Asbeck, “Design of Linear RF Outphasing Power Amplifiers”, (USA), Artech House, 2003
However, these LINC circuits each include two orthogonal modulators for generating the two periodic signals. The orthogonal modulators are large and exhibit significant drift due to temperature and processing. Accordingly, the LINC circuits have undesirably large structures and have difficulty outputting stable and accurate modulated signals.